Apparatus for casting



June 16; 1936; QM. KUETTEL 2,944,359 i APPARATUS FOR CASHNG 1 Filed July24, 193 2 Sheets-Sheet 1 INVENTOR. Glen M.Kue He] ATTO June 16, 1936. s.M. KUETTEL APPARATUS FOR CASTING Filed July 24, 1934 2 Sheets-Sheet 2INVENTOR. Glen MKveHel ATTORN Patented June 16, 1936 APPARATUS FORCASTING Application July 24, 1934, Serial No. 736,679

1 Claim.

This invention relates to an apparatus for easting and, moreparticularly, to an improved apparatus for casting polymerizable organicliquids.

There is a substantial class of organic liquids capable of beingpolymerized by suitable agencies to form solid resins of more or lessrigid character which, in the form of blocks, rods, tubes, and otherprimary shapes, are capable of being fabricated by machining processes,and the like, into useful articles of commerce. For the preparation ofthese so-called turnery resins it is desirable to effect thepolymerization of the initial materials in formsv or molds so as tosecure by means of a single operation either the primary shapes which inturn constitute the raw material for the fabrication of the ultimatearticle, or, in some cases, the shape of the ultimate article itself, ora close approximation thereto, which can be finished by a minimum ofmachining operations, polishing, and the like.

Unfortunately, however, serious obstacles to the successful formation ofresin shapes in this manner are offered by the considerable contractionin volume which takes place in these substances during, and as a resultof, their polymerization, and by the exothermic nature of thepolymerization reaction.

One result of the'exothermic nature of the polymerization reaction isthe formation of bubbles and internal flaws in the cast shape.Ostromislensky U. S. Patent 1,683,403 recognizes to some extent theproblem and suggests that, in casting rods and shapes more or less inthe nature of rods, the molds in which the resin is polymerized bedisposed horizontally rather than vertically. Although this suggestionby no means completely solves the problem, it is advantageous in castingarticles which are elongated in shape so that when the mold is disposedhorizontally the height of the mold cavity is not very great.

However, even where the Ostromislensky procedure may be employed toobtain shapes free of internal flaws, the contraction of the resinduring the polymerization results in a rod or other article ofincomplete cross section. Thus, in a mold of circular cross section, thepolymerized rod would be flat along the top. Accordingly, in theproduction of rods by the Ostromislensky procedure it is necessary toemploy a mold of larger diameter than that desired in the finishedproduct, and then from the incompletely shaped resulting rod a perfectrod of the desired diameter may be machined. Obviously, this entails anappreciable loss of polymerized resin and is uneconomical.

An object of the present invention is to provide a molding apparatuswherein polymerizable organic liquids may be polymerized and cast freefrom bubbles and shrinkage flaws. A further object is to provide such amold in which the pro- 5 portion of polymerized resin which must beremoved in order to obtain a product of perfect cross section is reducedto a minimum. Other objects of the invention will be apparent from thedescription given hereinafter.

The above objects are accomplished according to the present invention byconstructing an apparatus which comprises, in operative castingposition, a mold chamber proper substantially horizontally disposed withrespect to its major axis and having a cavity whose vertical section atright angles to its major axis is of the shape to be molded, a reservoirchamber disposed vertically above said mold chamber and communicatingwith the cavity thereof through a relatively narrow opening extendinghorizontally along the top of the mold chamber throughout substantiallythe complete length of saidcavity, and. means for introducing asubstantially liquid polymerizable composition into the mold chamber.

Specific embodiments of the invention are illustrated in theaccompanying drawings wherein:

Fig. 1 is a more or less diagrammatic perspec-' tive view of one end ofan apparatus for casting;

Figs. 1A and 1B are vertical sections along the lines |A|A and IBIB ofFig. 1;

Figs. 2A to 2D are vertical sections of the apparatus shown in Fig. 1indicating the level of the organic liquid being polymerized at variousstages of the polymerization cycle;

Figs. 3A and 3B are vertical sections through the polymerized solid bodyafter removal from the casting apparatus; I

Fig. 4 is a perspective view of an apparatus for manufacturing the moldshown in Fig. 5;

Fig. 5 is a perspective view of the mold, with cork inserted in the openend, made from the apparatus illustrated in Fig. 4;

Figs. 5A, 5B, and 5C are vertical sections along the lines 5A-5A; 5B5B;and 5C5C, respec- 45 V tively, of Fig. 5;

Figs. 6A, 6B, and 6C are vertical sections at right angles to the majoraxis of molds adapted to give different specific shapes with respect totheir vertical section;

Fig. '7 is a vertical section at right angles to the major axis of amold similar to that illustrated in Fig. 5 but with'a differently shapedreservoir. I

In the drawings like reference numerals refer to like parts throughout.-Reierring particularly to Figs. 1, 1A, and 1B, a mold is illustrated inoperative position, being disposed substantially horizontally to itsmajor axis. The mold comprises an elongated mold chamber proper I havinga cavity whose vertical section at right angles to its major axis is ofthe shape to be molded, and a reservoir chamber 2 disposed verticallyabove the mold chamber I and communicating with the cavity of moldchamber I through a relatively narrow opening 3 (shown in Figs. 1A and1B) which extends horizontally along the top of mold chamber lthroughout substantially the complete length of the mold chamber. Asshown in Fig. 1, one end of the mold is closed, and the other end, notillustrated, being left open for removal of the solid cast product and,if desired, for introduction of the liquid to be polymerized. Preferablythe liquid is introduced through a small opening in the top of theapparatus with the mold proper in horizontalposition. As explainedlater, means are provided for closing the open end of the mold so that,during polymerization, the mold may be entirely closed. To facilitateremoval of the cast product, the mold, including both mold chamber I andreservoir chamber 2, is tapered slightly outwardly from the closed endtoward the open end. This is illustrated in somewhat exaggerated form byFig. 1A and 1B, Fig. 1A showing a section of the mold on the line iA'|Aof Fig. 1 adjacent the closed end thereof while Fig. 1B shows the largersection on the line IB|B of Fig. 1 adjacent the open end of the mold.The taper may be very slight and may be eliminated entirely in moldsthat are to be broken apart for removal of the cast product.

The procedure with respect to use of the apparatus of the presentinvention will be described with reference to Fig. 1 to Fig 3B,inclusive. The mold is filled with a substantially liquid polymerizablecomposition 4, e. g. methyl alpha methacrylate, to substantially the topof the reservoir 2 as indicated in Fig. 2A, the open end of the moldclosed and the mold disposed horizontally with respect toits major axisin an oven maintained at 70-7 5 C. to polymerize the composition.- Theprocess of polymerization of .these polymerizable organic liquidsresults in a gradual increase in viscosity of the liquid and a gradualincrease in specific gravity thereof or, in other words, a gradualshrinkage.

As the shrinkage of the composition develops in the mold chamber properit is compensated by a corresponding fiow'of the composition from thereservoir chamber, with the result that during polymerization the moldchamber I remains filled, at all times while the level in the reservoirchamber 2 gradually falls as a result of the shrinkage. Thisisillustrated in Figs. 23, 2C, and 2D showing the lowering of the liquidlevel in successive stages of the polymerization as the shrinkageprogresses. If the dimensions and relative cross sectional areas of themold chamber i and reservoir chamber 2 of the mold have been properlycalculated with reference to the known shrinkage behavior of thematerial in question, there will remain, upon the completion orsubstantial completion of polymerization, a small excess of material inthe reservoir chamber 2, sufficient to provide the full cross sectionalarea of the desired circular rod. The polymerized product as removedfrom the mold will thus have the cross sectional configuration shown in-Fig. 3A. It is machined to the desired circular cross section as shownin Fig. 33 with a minimum loss of polymerized composition.

In the procedure described above, the reservoir chamber 2 had avolumetric capacity just slightly in excess of the volumetriccontraction of an amount of the polymerizable composition in questionequal to the volumetric capacity of the mold chamber 1. It will beunderstood that, in order to obtain a product of the full crosssectional area desired, it is necessary that the reservoir chamber 2have this slightly excess capacity and that it be filled. Obviously, areservoir chamber of greater capacity may be employed but, in

.that case, it is not completely filled asthe greatest economy iseffected in providing just suflicient polymerizable composition so thatupon substantially complete polymerization, the level of the resin willbe just sufiiciently high to insure a full cross sectional area of thedesired product.

In order to illustrate a practical embodiment of the invention, theprocedure for the construction and operation of a mold designed toproduce a circular rod of polymerized resin of diameter 0.75" from amaterial in which the shrinkage from monomeric to polymeric conditionamounts to 20% of the volume of the liquid monomer, will be given.

A master mold of metal, such as steel, is made which, when dipped intomolten lead. and then withdrawn therefrom, becomes coated with a solidlead jacket which, upon being stripped off the master mold, constitutesthe mold in which polymerization is eifected. In Fig. 4 a perspectiveview of this master mold is given. It

consists of a tapered cylindrical metal rod 6 to which is riveted orwelded a tapered triangular metal strip 1. These two parts may be madefrom one integral piece of metal. The junction of the metal strip 1 withthe cylinder 6 is made along the total length of one of the apexes ofthe strip 1. A slightly tapered metal plug 8 of circular cross sectionand of diameter equal to the combined height of the diameter of thecylinder 6 and triangular strip 1 is secured thereto in order to createa space in the open end of the lead mold that may be readily stopperedwith a cork, or the like. A handle 9 is provided for holding the mastermold while dipping it into the lead. The length ofthe master mold up tothe metal plug 8 was 14 and the master mold was provided with a taper of.016" in that length, the end of the mold adjacent the plug 8 being thelarger.

The ratio of the volume of the triangular strip I which will form thereservoir chamber of the mold and the volume of the cylinder 6 whichforms the mold chamber proper of the mold, is dependent upon the changeof density of the resin, or its shrinkage, as polymerization progresses.It was found that the cross sectional dimensions of a master mold formanufacturing resin rods of diameter from the material underconsideration required a reservoir chamber in which the section at rightangles to' its major axis was an incomplete equilateral triangle whoseinternal dimensions were /3" on a side at the small end of the mo d withthe diameter of the cylindrical rod 6%" and the width of the junctionbetween the two All of the joints and corners of the master cylinder.This permits ease of stripping the lead ,there is formed upon thespective in Fig. 5 and the mold on the line 5A 5A of Fig. 5 is shown inFig. 5A. In Fig. 5 a cork H is shown inserted in the open end In of themold. This is shown also in Fig. 5B which is a section on the line 5B-5Bof Fig. 5. The opposite end of the mold is a solid lead wall is asection on the line 5C5C of Fig. 5.

In the upper wall of the reservoir chamber 2 in Fig. 5 is drilled a holel2 having a diameter of for the purpose of filling the stoppered andhorizontally placed lead mold with the use of a funnel or some automaticloading device.

In operating the mold described, it is placed in horizontal positionwith respect to its major axis with the cork preferably covered withmetal foil, inserted firmly in the open end. The mold is then filledwith liquid monomer through the hole l2 which is then likewisestoppered. Alternatively, the hole l2 may be first stoppered and,holding the mold in vertical position, the liquid monomer may be pouredin the open end which is then plugged with the cork H before the mold isplaced in horizontal position. As shown in Fig. 5, the mold issubstantially horizontal with the reservoir chamber 2 vertically abovethe mold chamber l. The liquid monomer is then polymerized by theapplication of heat to the material and, upon completion ofpolymerization, the polymerized product may be removed through the openend of the mold.

The combined volume of the reservoir chamber and mold chamber of i alead mold created by a master mold of the dimensions given, excludingthe end stoppered with the cork, is 150 cubic centimeters. When such amold is completely filled with a monomeric methyl methacrylate withspecific gravity approximately 0.94 yielding a polymer of specificgravity approximately 1.2, a rod will result which is completelycylindrical, save for a minor, narrow, slightly elevated fin,

which may be easily removed. The percent waste.

of polymerized resin is substantially negligible.

The apparatus of the present invention has been described with respectto a mold adapted to produce rods but it is to be understood that themold cavity can be made in all variations of design to yield rods,tubes, or other shapes which may be cut into bracelets, napkin rings, orother shapes. Sections of various shaped molds at right angles to theirmajor axis areillustrated in Figs. 6A, 6B and 6C. The mold shown in Fig.6A is particularly adapted for the production of an annular rod to beused in the manufacture of bracelets, whereas Fig. 6B shows a mold ofspecial shape for clock cases and Fig. 6C a mold for producing apolygonal rod. These figures merely illustrate some of the infinitevariety of shapes which may be cast.

Those skilled in this art will understand that as indicated in Fig. 50which operating position of the" tween the two chambers it is notnecessary for the reservoir chamber 2 to have any plicity's sake aherein illustrated is usually employed.

In the polymerization of the organic liquids adapted for use in theapparatus of the present invention, it is preferable that no loss shalltake place through volatilization and, as a result, it is preferred thatThe width of this passage will, as a matter of economy, always berelatively narrow in order that the slightly elevated fin which mustalways result shall use as little polymerizable composition as possible.

In order that the flow of the material from the reservoir chamber intothe mold chamber shall not be obstructed, it is, of course, necessarythat the width of the passage between the two chambers be appreciable,with due considera tion being given to the her is approached. For terialthrough a relatively narrow passage beis possible until almost the endof the polymerization of the material in the mold chamber and, as aresult, all shrinkage in the mold chamber is compensated for.

While reference has been made specifically to the polymerization ofliquid methyl alpha methacrylate monomer, it is to be understood thatthe mold of the present invention is broadly applicable to polymerizablecompounds which shrink during polymerization. Other compounds of thisclass which may be mentioned include: ethyl methacrylate, butylmethacrylate, phenyl methacrylate, glycol di-methacrylate, vinylacetate, vinyl chloroacetate, acrolein, vinyl chloride, styrene,alpha-methyl styrene, methyl vinyl ketone, divinyl acetylene, ethyleneoxide, benzyl chloride, and dlmethyl itaconate.

' Many methods of polymerizing such compounds are well known in the useof heat, light, or polymerization catalysts, or some combination of thethree. Obviously the present method can be used regardless of the methodof polymerization. In applicant's copending application Serial No.736,678, entitled Preparation of cast resins, is described a particularmethod of polmerizing these compounds, layer by layer, to build up afinal product of any desired thickness. In this method each layerpolymerized is thin enough so that polymerization may be carried on at arelatively rapid rate without danger of formation of bubbles or otherart and usually involve the v it is possible to for the shrinkage involume of the final layer of compound.

In the production of cast articles in the mold of the present invention,it is by no means necessary that the polymerizable compound be introduced in the monomeric state, as partially polymerized material may beemployed-so long as it is fluid enough to accurately take the impressionof the mold. Where a partially polymerized material is being employed,it will be appreciated that the percentage of shrinkage will be lessthan where the monomeric compound is employed and, consequently, thecapacity of the reservoir chamber may be diminished.

The mold of the present invention may be used in the polymerization ofthese various compounds, either with, or without auxiliary agents suchas would occur to those skilled in the art, among which may be mentionedplasticizers, coloring matter both soluble and insoluble, variousmodifying resins both natural and synthetic, "effect materials, andsimilar ingredients in compositionsof this type.

The mold of the present invention can be used for the production of rodsand tubes from which finished articles are subsequently machined and forthe production of a limitless number of finished or semi-finishedarticles in individual molds.

By employing a mold such as herein described, obtain articles ofcomplete cross section regardless of the shrinkage coefficient of thematerial being polymerized, whereas this has not heretofore beenpossible in the molds held in centage of cases, make the productstotally unfit horizontal position during p lymerization for themanufacture of rods. and the like. Although this objection was not metin the manufacture of rods in molds held in vertical position, aspreviously 3 pointed out, it is'diificult to polymerize these 5compounds in appreciable depths without the formation of internalbubbles and other visible flaws which greatly detract from the value ofthe products obtained and, in fact, in a large perfor commercialpurposes.

As many apparently widely diiferent embodiments ofthis invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claim.

I claim:

Apparatus for casting substantially liquid polymerizable compositionscomprising, in operative 20 'position, an indivisible, integral moldchamber proper substantially horizontally disposed with respect to itsmajor axis and having a cavity whose vertical section at right angles toits major axis is of the shape to be cast, a lead reservoir chamber madeintegrally with the mold chamber and disposed vertically above said moldchamber and communicating with the cavity 01 the mold chamber through arelatively narrow opening extending horizontally along the top of themold chamber throughout substantially the complete length of saidcavity, the reservoir chamber in vertical section at right angles to itsmajor axis being substantially the shape of an equilateral triangle withone apex truncated by the opening 3 communicating with the mold chamberand said mold chamber and reservoir chamber being closed at one end andopen at the other and tapered slightly outwardly from the closed endtoward the open end, and removable means for closing said open endwhereby the polymerized product may be removed mm said mold chamber.

